The present invention relates to an exposure unit in an image recording apparatus, and more particularly to such an exposure unit for exposing a photosensitive pressure-sensitive recording medium to an image bearing light to form a latent image thereon. The latent image formed thereon is developed under pressure to thus provide a copied sheet.
Conventionally, image recording apparatuses have been known in the art. Some of such recording apparatuses use a transfer type recording medium described, for example, in U.S. Pat. No. 4,339,209. Generally, the transfer type image recording medium comprises a microcapsule sheet (first image recording medium) and a developer sheet (second image recording medium). The first image recording medium comprises a photosensitive pressure-sensitive recording medium provided with pressure rupturable microcapsules which encapsulate therein a first material (chromogenic material or dye precursor) having first and second phase dependent on light exposure. The second image recording medium comprises the developer medium provided with a second material (developer material) which provides an output image upon reaction with the first material. More specifically, in the first image recording medium, there are provided three kinds of microcapsules each encapsulating therein a chromogenic material of one of three primary colors; cyan, magenta and yellow. The cyan microcapsule contains a cyan chromogenic material as a primary component, a photo-curing (or photo-softening), resin, a photosensitizer, a photopolymerization initiator. The magenta and yellow microcapsules also contain the same components as those of the cyan microcapsule, but the cyan chromogenic material is replaced by magenta and yellow chromogenic materials, respectively.
In the image recording apparatus using the above-described recording medium, when exposure is taken place for the first medium, i.e. photosensitive pressure-sensitive recording medium, a filter unit is required to adjust color tone of the output image. This is partly because the sensitivities of the microcapsules to light differ depending upon the kinds of the microcapsules and partly because a light source for irradiating light onto an original has variations in light distribution. Furthermore, preference of color tone balance differs depending upon individuals, and one may want to adjust the color tone balance in the output image.
A conventional filter unit is disposed in such a manner that a filter is stretched perpendicular to an optical path to allow the entire cross-section of the light pass therethrough. Therefore, the color tone is not continuously adjustable and it is necessary to replace the filter when a different color adjustment is desired.
Another conventional filter unit has been known in which two filters are contained. Either one or both of the two filters are selectively inserted into the optical path by driving each associated drive source. Two light components of three primary colors of light are adjustable by those two filters relative to the remaining one primary color as a reference. In such a filter unit, however, the color adjustment cannot be adequately performed with respect to photosensitive pressure-sensitive recording mediums which have different characteristics in light sensitivity.
A still another conventional filter unit has been known in which two filters are contained and arranged to be horizontally movable. Each filter has two filter segments of different colors with a transparent region interposed therebetween, and one of the two filter segments in the respective filters are of the same color. The two filters are initially disposed in the optical path so that the light passes through the transparent regions. To adjust the color tone, the filters are individually horizontally moved to either of the directions so that two out of three primary colors are appropriately adjustable. However, such a filter unit is not efficient in that the two filters have the same type of the filter segments. Further, the size of the filter is enlarged du to the provision of two kinds of filter segments thereon, causing an increase in the overall size of the recording apparatus.